Biofunctional materials

ABSTRACT

Provided are methods and compositions for self-cleaning that include a digestive protein capable of decomposing stain forming molecules, a substrate applied to a solid surface, and a linker moiety bound to an outer surface of said substrate and an active group of said digestive protein, said linker moiety between said protein and said substrate and covalently linking said protein to a surface of said substrate by an amide bond, the linker moiety between a free amine of said protein and said outer surface of said substrate wherein the digestive protein forms a layer on a surface of said substrate such that the digestive protein is surface exposed for reaction with a stain.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/790,846 filed Oct. 23, 2017, which is a continuation of U.S. patentapplication Ser. No. 11/562,503 filed Nov. 22, 2006, the entire contentsof each of which are incorporated herein by reference.

FIELD

The present disclosure relates to self-cleaning compositions and aprocess for preventing and reducing surface stain accumulation due tobird droppings, bug wastes, food debris, and other stain causingmaterials.

TECHNICAL BACKGROUND

Both interior and exterior surfaces of automobile, such as coatings,paints, and seat fabrics, are subject to contamination and corrosionswhen they are under prolonged exposure to bird dropping, insect debris,resins of conifer, microbes, gums, etc. Certain stains, such asinsect-originated stains, are hard to remove with regular automaticbrush-free washing. Interior surfaces and coatings may also be easilyget stained with oil, protein, sugar and other ingredients in foods andbeverages, and timely removal of such stains may present certainchallenges.

Here, the present invention specifically involves the incorporation ofdigestive proteins including lysozymes, proteases, lipases, cellulases,etc., onto surfaces such as paints and coatings. The catalytic activityof the digestive proteins enables ongoing self-cleaning to reduce andeliminate stain contaminations. The mechanism of action of thesedigestive proteins is mainly enzymatic in nature and does not involvethe use of any corrosive or oxidative components; therefore, they areenvironmentally friendly.

Stains of interests in the initial stage of this work include thoseformed from broken bodies of bugs, animal (like bird) wastes, foods,milk and other beverages, and cosmetic and personal care products.Although the detailed components vary with sources of stains, the majorcomponents of stains that are adhesive to surfaces are proteins,polysaccharides, fats or oils.

DESCRIPTION OF RELATED ART

It is known to incorporate enzymes into coating or into substrates forthe purpose of providing a surface with antimicrobial, antifungal orantifouling properties. Yet it is novel to the best knowledge ofApplicants to attach digestive proteins to a surface for the purpose ofenzymatically decomposing stain molecules in contact with the surface.

U.S. Pat. No. 6,818,212 discloses an enzymatic antimicrobial ingredientfor disinfection and for killing microbial cells.

Wang et al. 2001 discloses lifespan extension of an enzyme upon itscovalent binding at wet conditions; yet the reference does not seem tomention the utilization of such covalently bound enzyme in the area ofsurface self-cleaning.

U.S. Pat. No. 3,705,398 discloses polymeric articles having activeantibacterial, antifungal and combinations of antibacterial andantifungal properties. The antibacterial and antifungal activatingagents are distributed within the polymeric composition and migrate tothe surface.

U.S. Pat. No. 5,914,367 discloses a method of preparing apolymer-protein composite including polymerizing a monomer in thepresence of a protein dissolved in an organic phase via the ion-pairingof the protein with a surfactant. This reference, however, does not seemto mention the prevention or reduction of stain accumulation using thedigestive power of such a polymer-protein composite.

U.S. Pat. No. 6,150,146 discloses a method of releasing a compoundhaving antimicrobial activity from a matrix at a controlled rate. Themethod includes an enzyme and a substrate within the matrix beforehandto allow the enzyme and substrate to react with each other in thematrix, thereby to produce a compound having antimicrobial activity. Thepatent also discloses a coating composition comprising a film-formingresin, an enzyme, a substrate and any enzyme capable of reacting withthe substrate.

U.S. 2005/0058689 discloses paints and coatings having antifungal growthand antibacterial materials. Specific chemicals and formations aredisclosed for incorporation into painted surfaces which are antifungalcompositions to inhibit growth of mold, bacterial, and fungi on buildingmaterials.

The object of the present invention is to provide self-cleaningcomposition and process containing digestive proteins for preventing andreducing stain accumulation.

SUMMARY

The following summary of the invention is provided to facilitate anunderstanding of some of the innovative features unique to the presentinvention and is not intended to be a full description. A fullappreciation of the various aspects of the invention can be gained bytaking the entire specification, claims, drawings, and abstract as awhole.

Provided are compositions for self-cleaning of a stain that include asubstrate, a digestive protein capable of decomposing a stain molecule,and a linker moiety between the substrate and the digestive protein,where the linkage is or is between a free amine on the digestive proteinand the substrate.

The compositions as provided herein may be useful as a mechanism toprevent the accumulation of contacting stains and dirt by an “automatic”enzymatic degradation reaction. The digestive proteins of thecomposition may include proteases which hydrolyze protein molecules,lipases which hydrolyze lipids and fats, cellulases which hydrolyzecellulose, and amylases which hydrolyze carbohydrates, etc. It isneither required nor necessary for the digestive proteins to have theirfunctional binding pockets all facing towards stain particles. A layerof digestive proteins delivers enough coverage and digesting activityeven though the digestive proteins may be randomly arranged on asurface.

Optionally, a surface may be pretreated with a layer of polymercomprising one or more active groups. A digestive protein suspension maybe spin coated onto the polymer layer with the active groups to formcovalent bonds between the proteins and the polymer layer. The activegroups may comprise alcohol, thiol, aldehyde, carboxylic acid,anhydride, epoxy, and ester, etc. Alternatively, digestive proteins maybe attached to nanoparticles before their suspension with paints orcoatings.

BRIEF DESCRIPTION OF DRAWINGS

The present invention is further illustrated by reference to theaccompanying drawings, in which

FIG. 1 is a depiction of an attachment of enzymes to the surface ofpolymeric nanoparticles.

FIG. 2 is a depiction of fluorescence images of protease coatingprepared via adsorption and covalent cross-linking.

FIG. 3 shows a protein assay calibration curve.

FIG. 4 shows a calibration curve for tyrosine (product of hydrolysis).

FIG. 5 shows a representative GPC chromatograph indicating egg whitestain degradation.

FIG. 6 shows the time course of egg white stain degradation.

FIG. 7 shows thermal stability of protease coating at 80° C.

DETAILED DESCRIPTION

The present disclosure relates to, in a first aspect, a compositioncomprising a substrate, a digestive protein capable of decomposing astain molecule, and a linker moiety.

This disclosure specifically involves the incorporation of one or moredigestive proteins including lysozymes, proteases, lipases, cellulases,etc., onto surfaces such as paints and coatings. The catalytic activityof the digestive proteins enables ongoing self-cleaning to reduce andeliminate stain contaminations.

Various stains include those formed from broken bodies of bugs, animal(such as bird) wastes, foods, milk and other beverages, and cosmetic andpersonal care products. Although the detailed components vary withsources of stains, the major components of stains that are adhesive tosurfaces are proteins, polysaccharides, fats or oils.

The activity of the digestive proteins toward different stain sourcesmay be evaluated in a solution environment. Tests are conducted atdifferent conditions including different pH and temperature, in anattempt to evaluate the proteins' performance in an automobileenvironment instead of that in a washer machine as they have beentraditionally applied. Tests include: protein-related activity;starch-related activity tests; tests with oily stains. Protein activityunit is defined as: one unit of digestive protein hydrolyzes casein toproduce absorbance difference equivalent to 1.0 μmol of tyrosine perminute at 37° C. under the conditions of the assay. Results of activityassay show covalent cross-linked protease present an activity that isnine times more than that of a physically absorbed protease.

There are several ways to incorporate the digestive proteins onto asubstrate. One of which involves the application of covalent bonds.Specifically, free amine groups of the digestive proteins may becovalently bound to an active group of the substrate. Such active groupsinclude alcohol, thiol, aldehyde, carboxylic acid, anhydride, epoxy,ester, or any combination thereof. This method of incorporatingdigestive proteins delivers unique advantages. First, the covalent bondstether the proteins permanently to the substrate and thus place them asan integral part of the final composition with much less, if not at all,leakage of digestive protein species. Second, the covalent bonds providefor extended enzyme lifetime. Over time, proteins typically loseactivity because of the unfolding of their polypeptide chains. Chemicalbinding such as covalent bonding effectively restricts such unfolding,and thus improves the protein life. The life of a protein is typicallydetermined by comparing the amount of activity reduction of a proteinthat is free or being physically adsorbed with that of a proteincovalently-immobilized over a period of time. Results have shown that aprotein that is in free form or being physically adsorbed to a substrateloses its activity much faster that a protein in covalent-bond form.

Alternatively, digestive proteins may be uniformly dispersed throughoutthe substrate network to create a homogenous protein platform. In sodoing, digestive proteins may be first modified with polymerizablegroups. The modified proteins may be solubilized into organic solventsin the presence of surfactant, and thus engage the subsequentpolymerization with monomers such as methyl methacrylate (MMA) orstyrene in the organic solution. The resulted composition includesdigestive protein molecules homogeneously dispersed throughout thenetwork.

Also, digestive proteins may be attached to surfaces of a substrate incomparison to the above mentioned cross-linking methods. An attachmentof digestive proteins corresponding to ˜100% surface coverage wasachieved with polystyrene particles with diameters range from 100 to1000 nm.

The digestive proteins of the composition may include proteases whichhydrolyze protein molecules, lipases which hydrolyze lipids and fats,cellulases which hydrolyze cellulose, and amylases which hydrolyzecarbohydrates. It is neither required nor necessary for the digestiveproteins to have their functional binding pockets all facing towardstain particles. A layer of digestive proteins delivers enough coverageand digesting activity even though the digestive proteins may berandomly arranged on a surface.

Optionally, a surface is pretreated with a layer of polymer comprisingone or more surface active groups of succinimide ester. A digestiveprotein suspension is spin coated onto the layer of the polymer with theactive groups to form covalent bonds with the proteins. Alternatively,digestive proteins may be attached to nanoparticles before theirsuspension with paints or coatings.

This disclosure is further directed to a composition comprising adigestive protein capable of decomposing a stain molecule, and a coatingsubstrate wherein the digestive protein may be entrapped in the coatingsubstrate. In this composition, the digestive protein may be selectedfrom lysozymes, proteases, lipases, cellulases, glycosidases, andamylases.

In another aspect of this disclosure, a process is disclosed forreducing and or eliminating stain contaminations. The process comprisesbinding a substrate to a surface and forming a linker moiety between anactive group of a digestive protein and the substrate. In this process,the substrate may comprise surface active groups such as alcohol, thiol,aldehyde, carboxylic acid, anhydride, epoxy, ester, and any combinationsthereof.

Example 1

Enzymes may be attached to surfaces of plastics. An enzyme attachmentcorresponding to ˜100% surface coverage may be achieved with polystyreneparticles with diameters range from 100 to 1000 nm. By coating withdigestive protein, these particles may be used along with paints orcoatings to functionalize the surfaces of materials. The same chemicalbonding approach may be applied to coat enzymes onto preformed plasticparts, and thus form a protein coating on the parts' surfaces. As shownin FIG. 1, particles with diameters ranging from 100 nm to 1000 nm maybe synthesized by emulsion polymerization. Emulsion polymerization is atype of polymerization that takes place in an emulsion typicallyincorporating water, monomer, and surfactant. The most common type ofemulsion polymerization is an oil-in-water emulsion, in which dropletsof monomer (the oil) are emulsified (with surfactants) in a continuousphase of water.

Particles as previously described may be synthesized by mixing anaqueous solution (mixture of water and ethanol, ˜20 ml), containing apolymerizable surfactant (2-sulfoethylmethacrylate), a stabilizer(polyvinylpyrrolidone, PVP) and an initiator (2,2′-Azobis[2-methyl-N-(2-hydroxyethyl) propionamide]), will be mixed with anorganic solution (˜1 ml) of styrene, N-acryloxysuccinimide (NAS, afunctionalized vinyl monomer), and divinyl benzene (˜1% v/v). Theparticle size may be controlled by adjusting phase ratio (1/30˜1/15,oil/aqueous) and the concentration of ethanol (0.125˜0.50 ml/ml),2-sulfoethyl methacrylate and PVP (0˜5.5 mg/ml). The reaction may beperformed with stirring at 70° C. for 10 h, followed by washing theresulted particles with ethanol and DI water in a stirredultrafiltration cell with a polyethersulfone membrane (cut off MW: 300kDa).

Example 2

Stains may be generated from different sources of contacts. Bodyresidues of bugs, animal wastes, food, milk and other beverages, andcosmetic and personal care products may all cause stains. Although thedetailed components vary with sources of stains, the major componentsthat are adhesive to surfaces are proteins, simple sugars andpolysaccharides, fats and/or oils. Digestive proteins including lipases,proteases, amylase and cellulose, each of them attacks differentcomponents, are thus far the most effective, safe and economic agents tofight against such stains. As shown below in Table 1, these proteinswere examined and tested in our initial screening tests, and eventuallywe selected protease to proceed for the majority of the subsequentexperiments due to the easiness in activity measurement.

TABLE 1 Targeting Standard testing Enzyme Stains Source Functionsconditions Proteases Bugs, dairy Bacillus Hydrolysis of Casein withFolin & products, animal licheniformis proteinaceous Ciocalteu's Phenolwastes (Subtilisin Carlsberg) materials dye, pH 7.5, 37° C., absorbanceat 660 nm Lipase Fats and oils, Pseudomonas Hydrolysis of p-nitro phenylAK cosmetics, inks fluorescens oils and fats valerate, pH 7.7, 40° C.,absorbance at 405 nm α- Juices, soft Bacillus subtilis Hydrolysis ofDyed Starch, pH 6.9, Amylase drinks, foods, starch 25° C., absorbance atanimal wastes 540 nm Cellulase Beverages, Aspergillus niger Hydrolysisof Dyed cellulose, pH foods, animal cellulose 6, 50° C., absorbancewastes, at 590 nm

Example 3 Preparation of Enzyme Coating

N-acryloxy succinimide (392 mg), 1.2 ml of styrene and 29.2 mg of4,4′-azobis-(4-cyanovaleric acid) were mixed with 16 ml of chloroform ina 20 ml glass reaction vial. The vial was purged with nitrogen, sealedand incubated at 70° C. for 12 hrs with stirring, followed by theremoval of solvent by purging nitrogen. The polymer product wasre-dissolved in chloroform at a concentration of 50 mg/ml. Onemilliliter of the resulting solution was spin-coated onto a polystyreneplate (11 cm in diameter) at 6000 rpm. Protease from SubtilisinCarlsberg was dissolved in 0.05 M phosphate buffer at a concentration of10 mg/ml. The enzyme was applied onto the active polymer coated platevia 3-step layer-by-layer spin coating: 1) 1 ml of the proteasesolution, 2) 1 ml of protease solution containing 0.5% (V/V) ofglutaraldehyde, 3) 1 ml of protease solution. The spin-coated plateswere kept at 4° C. for 12 h, followed by extensive washing with 0.05 MTris buffer (pH 8), 2M NaCl solution and DI water. Finally the plateswere air-dried and cut into small pieces (1×2 cm). This method wasdesignated as covalent cross-linking. As a comparison, similar procedurewas applied on a polystyrene plate without the active polymer coating,which was called as physical adsorption.

Example 4 Visualization of Enzyme Coating

Fluorescent dye (Oregon green, Invitrogen Corp.) was first dissolved indimethyl sulfoxide at a concentration of 2 mg/ml. The sample plates withphysically adsorbed and covalently immobilized enzyme were incubated inthe dye solution at room temperature with gentle shaking for 2 hours,followed by rinsing with DI water. The plates were then dried innitrogen and observed under a fluorescence microscope. The images areshown in FIG. 2, where green color denotes the area covered with enzyme.Compared with physical adsorption, much more enzyme was immobilized onthe surface using covalent cross-linking method.

Example 5 Determination of Enzyme Loading

The amount of enzyme attached to the plastic plate was determined by areversed Bradford method. Typically, a working solution was firstprepared by diluting Bradford reagent with DI water (1:5, by volume). Acalibration curve was first obtained using free protease as thestandards. In a 1 ml cuvette, 0.5 ml of protease solution was mixed with0.5 ml of the working solution and then allowed to react for 5 min. Theabsorbance of the solution was measured at 465 nm on aspectrophotometer. After testing a series of different proteaseconcentrations, a calibration curve was obtained as shown in FIG. 3.

To determine the loading of immobilized enzyme, a piece of enzyme-coatedplate (1 cm×2 cm) was placed into a 20-ml glass vial, followed by theaddition of 0.5 ml of DI water and 0.5 ml of the working solution. Thevial was slightly agitated for 5 min at room temperature to allowbinding of the dye to the immobilized enzyme. The absorbance of thesupernatants was then recorded at 465 nm. Similarly a blank plasticplate without enzyme coating was also measured as the control. Thereading obtained with the blank plate was subtracted from the readingobtained from the enzyme loaded plate. Comparing the obtained readingdifference with the calibration curve gave the loading on the plate,which was then normalized into a unit of μg/cm². The enzyme loading bycovalent cross-linking and physical adsorption were 8.5 and 1.0 μg/cm²,respectively.

Example 6 Verification of the Proteolytic Activity of Enzyme Coating

Enzyme in solution: The proteolytic activity of protease was determinedusing 0.65% (w/v) casein as the substrate. Protease solution (0.1 ml)was incubated with 0.5 ml of casein solution for 10 min at 37° C. Thereaction was stopped by the addition of 0.5 ml of tricholoroacetic acid(110 mM). The mixture was centrifuged to remove the precipitation. Theresulting supernatant (0.4 ml) was mixed with 1 ml of sodium carbonate(0.5 M) and 0.2 ml of diluted Folin & Ciocalteu's phenol reagent (1:4 bydiluting Folin & Ciocalteu's phenol reagent with DI water), followed byincubation at 37° C. for 30 min. Finally the mixture was centrifugedagain and the absorbance of the supernatant was measured at 660 nm on aspectrophotometer. Blank experiment was performed without enzymesolution by adding 100 μl of buffer and carrying out similar test. Theabsorbance of the blank was subtracted from the sample (enzymesolution).

The activity unit was defined as: one unit of enzyme hydrolyzes caseinto produce absorbance difference equivalent to 1.0 μmol of tyrosine perminute at 37° C. under the conditions of the assay. Tyrosine amino acidwas used for calibration. Various concentrations of tyrosine werereacted with Folin-Ciocalteau reagent and the resulting calibrationcurve is shown in FIG. 4.

Enzyme coating: The activity of the immobilized protease was determinedin a similar manner by using an enzyme coated polymer piece (1×2 cm)instead of enzyme in solution and a blank polymer coated piece ascontrol. The activity of protein was termed as surface activity per unitarea.

Results of activity assay showed that plates with covalent cross-linkedprotease afford 5.6×10⁻³ unit/cm², while physical adsorbed enzyme onlydisplayed an activity of 0.6×10⁻³ unit/cm².

Example 7 Stain Degradation on Enzyme Coating

Egg white was used as the model stain to determine the stain degradationon enzyme coating. Onto a plate (11 cm in diameter) withprotease-coating, 2 ml of egg white solution (10 mg/ml in DI water) wasspin-coated at 2000 rpm. The plate was then cut into smaller pieces (1×2cm) and kept at room temperature (25° C.) for various period of time toallow the degradation of egg white. After certain intervals, one smallplate was carefully washed with DI water and the egg white in thewashing solution was analyzed using gel permeation chromatography (GPC)to determine the molecular weight changes. Typically two peaks werefound in the GPC chromatograph (FIG. 5): one has shorter retention timeand the other has longer retention time, corresponding to the egg whiteand degradation products, respectively. Based on the area of the eggwhite peaks, a time course of egg white degradation was obtained asshown in FIG. 6. Control experiments were also performed using plateswithout protease coating, but no clear product peaks were identified.

Example 8 Thermal Stability of the Enzyme Coating

Thermal stability of the enzyme coating was studied at 80° C. in anair-heating oven. At certain time intervals, the sample plate(s) weretaken out of the oven and the activity were measured following theprocedure as described in Working Example 2. The decrease of activitywith time was plotted in FIG. 9. It appeared that covalent cross-linkedenzyme afforded better stability against thermal inactivation, ascompared to physical adsorbed enzyme.

Various modifications of the present invention, in addition to thoseshown and described herein, will be apparent to those skilled in the artof the above description. Such modifications are also intended to fallwithin the scope of the appended claims.

It is appreciated that all reagents are obtainable by sources known inthe art unless otherwise specified or synthesized by one of ordinaryskill in the art without undue experimentation.

Patents and publications mentioned in the specification are indicativeof the levels of those skilled in the art to which the inventionpertains. These patents and publications are incorporated herein byreference to the same extent as if each individual application orpublication was specifically and individually incorporated herein byreference.

The foregoing description is illustrative of particular embodiments ofthe invention, but is not meant to be a limitation upon the practicethereof. The following claims, including all equivalents thereof, areintended to define the scope of the invention.

1. A process for self-cleaning, comprising: binding a digestive proteinto the surface of a substrate, the digestive protein capable ofdecomposing a stain forming molecule; the digestive protein bound to thesurface by a linker moiety between an active group of the digestiveprotein and said substrate, said active group comprising a free amine;and the digestive protein forming a layer on the surface such that thedigestive protein is surface exposed for self-cleaning of a staincomprising one or more of said stain forming molecules.
 2. The processaccording to claim 1, wherein said substrate comprises one or moreselected from the group consisting of alcohol, thiol, aldehyde,carboxylic acid, anhydride, epoxy, and ester.
 3. The process accordingto claim 1, wherein said surface is selected from the group consistingof metal, glass, paint, plastic, and fabrics.
 4. The process accordingto claim 1, wherein said free amine is a lysine, arginine, asparagine,glutamine, or an N-terminal end.
 5. The process according to claim 1,wherein the self-cleaning of a stain molecule by said digestive proteinoccurs in a dry environment.
 6. The process of claim 5, wherein an endproduct of said decomposing is removable by water or rain.
 7. Theprocess according to claim 1, wherein the digestive protein comprises alysozyme, protease, lipase, cellulase, glycosidase, or amylase.
 8. Acomposition for removing stains from a solid surface comprising: adigestive protein capable of decomposing stain forming molecules; asubstrate applied to the solid surface; and a linker moiety bound to anouter surface of said substrate and an active group of said digestiveprotein, said linker moiety between said protein and said substrate andcovalently linking said protein to a surface of said substrate by anamide bond, the linker moiety between a free amine of said protein andsaid outer surface of said substrate; said digestive protein forming alayer on a surface of said substrate such that the digestive protein issurface exposed for reaction with a stain.
 9. The composition accordingto claim 8, wherein the digestive protein comprises a lysozyme,protease, lipase, cellulase, glycosidase, or amylase.
 10. Thecomposition according to claim 8 wherein said free amine is in a lysine,arginine, asparagine, glutamine, or an N-terminal end.
 11. Thecomposition according to claim 8, wherein the digestive proteincomprises a lipase.
 12. The composition according to claim 8, whereinsaid substrate comprises paint or polymers.